Okay, I have read the info that provides by Maguscreed.
We need to obtain a genuine XP installation media.
which means, we have 2 license key here, isn't it?
First key is the Windows 7 Professional or Ultimate's product key.
Seceond key is the Windows 7 Professional or Ultimate's product key.
Using the XP installation media to install XP, which will Format 1 of the drive to install XP.
This is just like no different with wiping Windows 7 and install XP.
an ordinary drive format and clean install?